1. Field of the Invention
This invention relates to a combustion chamber for internal combustion engines, and more particularly to a combustion chamber suitable for an internal combustion engine operating on a fuel of a low cetane number such as gasoline, alcohol or the like.
2. Prior Art
Generally, in the case where a fuel oil is injection into a combustion chamber directly as in Diesel engines or the like, it is necessary to properly mix the fuel with air in order to improve the quality of combustion.
However, where the injected fuel oil is a volatile fuel oil of a low cetane number like alcohol or gasoline, the fuel volatilizes and disperses as soon as it is injected into the combustion chamber due to its high volatility, and thereby forms a lean air-fuel mixture therein. Therefore, problems arise in terms of ignition quality and flame propagation quality even if a forced ignition means like a spark plug is used. These problems become worse expectially under light load operation with a reduced amount of fuel injection. In this connection, it is possible to choke the intake air as a countermeasure, but this is however undesirable because of degradations in output and mileage qualities of the engine which result due to the additional pumping effort required of the engine to throttle the intake air.
In an attempt to eliminate these problems, the present inventors proposed in their co-pending Japanese patent application No. 60-106944 an improved combustion chamber for internal combustion engines.
As illustrated in FIG. 7 of the accompanying drawings, the just-mentioned prior application employs communicating main and subsidiary combustion chambers 2 and 3 which are formed side by side by hollowing a piston top 1, a fuel injection nozzle 4 disposed in the main and subsidiary combustion chambers 2 and 3 for injecting a fuel thereinto, and an ignition means 15a provided in the subsidiary combustion chamber 3 for igniting the injected fuel.
This arrangement attempts to enhance the combustion quality by confining a volatile fuel oil along with a swirl in the subsidiary combustion chamber of a smaller volume under light load operation to maintain an minimum air-fuel ratio for ignition by the ignition means, while under medium and high load operations propagating flame through a bank portion to the fuel oil which is injected and volatilized in the main combustion chamber.
However, the existence of the bank portion which restricts the entrance of the volatilized fuel oil into the main combustion chamber from the subsidiary combustion chamber has the effect of slightly delaying the velocity of flame propagation into the main combustion chamber under medium and high load operations, thereby lowering the output and mileage qualities to an extent corresponding to the delay. It is therefore necessary to solve these problems in order to attain combustion quality comparable to gasoline engines.